Conventionally, a rotary electric machine used as a generator or a motor in vehicles has a rotor and a stator disposed facing the rotor in a radial direction.
The stator has a stator core with a plurality of slots aligned in a circumferential direction, and a stator winding wound around the slots of the stator core.
In this rotary electric machine, when an electric current flows through the stator winding, the stator winding and the stator core generate heat.
When the heat is generated in this way, a magnetic flux generated in the rotary electric machine is affected, and reduces an operating efficiency of the rotary electric machine.
Therefore, in order to maintain a high operational efficiency, it is necessary to cool the rotating electric machine, and a rotating electric machine having a cooling structure is proposed in Japanese Patent Application Laid-Open Publication No. 2005-12961, for example.
On the assumption that the rotating electric machine is mounted in a vehicle so that its axial direction becomes horizontal, a groove extending in a circumferential direction to induce a coolant is formed on a circumferential surface of a coil-end of the stator winding that projects from the stator core to both sides in the axial direction in the cooling structure disclosed in the Publication '961.
In this case, by dropping a coolant such as oil to the coil-end of the rotating electric machine that is mounted horizontally, the coolant is adapted to flow along the circumferential surface of the coil-end.
By the way, a segment-type stator winding formed by connecting a plurality of U-shaped conductor segments, for example, as the stator winding is known.
In the stator winding of this kind, conductor wires of the coil-end become interlaced, and thus relatively large gaps are formed between the conductor wires.
Therefore, when this kind of the stator winding is employed, the coolant such as the oil or the like would fall in a vertical direction from the gaps between the conductor wires even when the groove is formed on the circumferential surface of the coil-end as disclosed in the Publication '961 above, it is impossible to obtain a sufficient cooling effect.
As a result, there is a possibility that an insulating film covering the surface of the stator winding is melted, causing insulation failure.